There has heretofore been known a replacement apparatus for replacing electrode tip of a welding gun, as disclosed in the Japanese Unexamined Utility Model Registration Application Publication, Jikkai Sho 62-165084. In such apparatus, a pair of electrode tips, attached to a pair of gun arms of a welding gun, are each provided with an engagement portion. An electrode coupler connects both the electrode tips to each other by engaging with the engagement portions when the welding gun is applied with pressure. The electrode tips can be pulled off from the respective gun arms, when the welding gun is operated, to open the gun arms.